1. Field of the Invention
The present invention generally relates to a projection apparatus, in particular, to an illumination system of a projection apparatus.
2. Description of Related Art
Referring to FIG. 1 a conventional illumination system 100 of a projection apparatus includes a laser light source 100, a lens group 120 and a reflecting mirror 130. The laser light source 110 is used for providing a light beam 112. The lens group 120 is disposed at a transmission path of the light beam 112 for condensing the light beam 112. The reflecting mirror 130 is disposed at the transmission path of the light beam 112 for reflecting the light beam 112 to a light valve 50 of the projection apparatus.
Because the light beam 112 provided by the laser light source 110 easily occurs interference, speckle patterns are frequently occurred on the light valve 50 when the light-beam 112 is projected onto the light valve 50. This is the so-called speckle noise. To reduce the speckle noise, an actuator (not drawn) is used in the conventional technique to drive the reflecting mirror 130 into swinging motion between angles of ±θ about an axis. Hence, the location of the light beam 112 projected on the light valve 50 is changed and speckle noise is reduced. However, because the reflecting mirror 130 is allowed to swing with respect to only one axial direction, the range of variation of the location of the light beam 112 on the light valve 50 is quite limited. As a result, the effect on lowering the speckle noise is also limited.
The conventional technique also includes a method of driving the reflecting mirror 130 to swing in two mutually perpendicular axes. Setting the reflecting mirror 130 to swing in two axial directions is capable of increasing the range of variation of the location of the light beam 112 on the light valve 50 and obtaining better speckle noise reduction. However, setting the reflecting mirror 130 to swing in two axial directions normally requires two actuators and a more complicated control circuit. Therefore, the fabrication cost is increased.